Apply bubble bar background alpha to stroke paint

Alpha was applied to fill paint only. Add it to stroke paint as well.
Introduce a new method in Utilities to map range of ints and not only
floats.

Bug: 345687278
Test: compare bubble bar shadow and stroke before and after change
Flag: com.android.wm.shell.enable_bubble_bar

Change-Id: I7c9e8d6337a857a661de0c945181cdd5ef2fd4ca